GOVERNANCE.md: fix the release version number check (#4803)
GOVERNANCE.md: fix the release version number check (#4803)

The VERSION file is relevant for Envoy (where this document is based on).
Such file does not exist for TiKV, and the version is recorded in
Cargo.toml. Updated the instruction to refer to Cargo.toml not VERSION.

Signed-off-by: kennytm <d10ee62456d8e2be8715605d23b69b7662d1915a@gmail.com>
BusyJay/tikv,BusyJay/tikv,pingcap/tikv,BusyJay/tikv,c4pt0r/tikv,BusyJay/tikv,pingcap/tikv